This invention is concerned with a drive system for a glass container production line.
The dominant type of machine used for the production of glass containers is the individual section type. In such a machine, a plurality of individual container forming units, or sections, are arranged side by side, are fed with gobs of molten glass from a common source, and feed their production to a common conveyor system. The sections are fed with gobs in a predetermined sequence and, at any given moment, one section is receiving a gob while the others are at different stages of their operation.
In a glass container factory, molten glass is produced by a furnace and is fed through forehearths to one or more production lines. Each production line comprises a feeder operable to produce gobs from molten glass delivered to the feeder from the furnace, a glass container manufacturing machine of the individual section type having a plurality of sections each of which is operable to mould gobs delivered thereto into glass containers, a gob distributor operable to distribute successive gobs produced by the feeder to the sections of the machine in a predetermined sequence, a conveyor system operable to carry completed containers away from the machine, and transferring means operable to transfer completed containers from the machine to the conveyor system, such transferring means being generally known as push-out means as the containers are pushed out on to a conveyor of the conveyor system. In some cases, two machines, with associated feeders, gob distributors and transferring means, operate to feed their output to the same conveyor system. A first conveyor of the conveyor system runs transversely of the sections and conveys the containers to ware-transferring means, usually provided by a transfer wheel, which removes the containers from the first conveyor and positions them on a second, or cross, conveyor which conveys them to a lehr in which the containers are heat-treated. Clearly, it is necessary that the operations of the feeder, the gob distributor, the machine and the transferring means are synchronised so that each gob produced can be moulded into a container which is transferred to the conveyor system. It is equally clear that the operations of the first conveyor, the ware-transferring means, and the second conveyor have to be synchronised so that each container can be conveyed to the lehr. Furthermore, the speeds of the machine and of the conveyor system have to be related so that the conveyor system can accommodate each container produced with an appropriate spacing between successive containers on the conveyor system. In order to achieve appropriate speeds, a drive system for the production line is used.
In a conventional drive system, at least the feeder, the gob distributor and the conveyor system are driven by A.C. electrical motors which operate at a speed dependent on the frequency of the power supply thereto. A single frequency is supplied to all the motors and this frequency is varied to speed up or slow down the entire production line. The motors drive their various mechanisms via gear arrangements which are arranged to synchronise with one another when the motors run at the same speed, i.e. when the motors receive power supplies with the same frequency. The machine itself, if it is of an older type, is timed by cams mounted on a timing drum driven by a further motor of the drive system which receives the single frequency, or, if it is of a newer type, is operated by a timing system which receives clock pulses produced by operation of one of the motors of the drive system, usually the feeder motor. Thus, increasing or decreasing the single frequency causes a corresponding change in the frequency of the clock pulses and hence keeps the machine in synchronisation. The transferring means may be driven by a further electrical motor of the drive system or may be operated by the timing system of the machine. The first conveyor, the ware-transferring means and the second conveyor of the conveyor system are driven by individual electrical motors of the drive system which all receive the single frequency.
With the conventional drive system described above, it is relatively easy to speed up or slow down the entire production line by varying the single frequency. However, any change in the relative speeds of the various parts of the production line requires changing the gear ratios. Furthermore, fine tuning of the system in operation is not possible. Thus, no change can be made in any speed without altering all the others. One disadvantage is that, if one of the sections goes out of use for a significant length of time, it is not possible to slow the feeder to produce less gobs as this would slow the other sections of the machine and upset the thermal balances in the sections necessary to correct moulding. In practice, this situation is dealt with by throwing away the gobs intended for the out-of-use section which is undesirable as the energy used in melting the glass is wasted. Another disadvantage is that wear on the gears can upset the synchronisation of the parts of the production line and compensation for this wear cannot be achieved during production.
A drive system is described in U.S. Pat. No. 4,007,028 which would overcome some of the disadvantages of the conventional drive system described above but which would introduce the further disadvantages mentioned below. In this system, there is a variable basic frequency source which is connected to adjustable multipliers associated with electrical motors driving the feeder, the gob distributor and the first conveyor. The multipliers each multiply the basic frequency by a different variable factor so that the speed of its associated motor can be varied independently. Variation of the basic frequency alters all the speeds so that the entire production line can be speeded up or slowed down. The speeds of the feeder, the gob distributor and conveyor can be individually adjusted to bring the production line to synchronisation. This system would avoid gear changes and allows fine tuning during operation. However, this system would have the disadvantages that it would be complicated to adjust and that it would be objectionable on safety grounds since there is not necessarily any correlation between the feeder and the gob distributor so that gobs could be produced at times when the gob distributor is not pointing at any of the sections.
It is an object of the invention to provide a drive system for a glass container production line which avoids gear changes and can be fine tuned during operation and which is simple to adjust and not objectionable on safety grounds.